Drive assemblies for coupling through pressure vessel barriers are known, see for example Canadian Pat. Nos. 1,020,614 issued Nov. 8, 1977 and 1,051,964 issued Apr. 3, 1978 both of which are assigned to the assignee of the present invention. However, such assemblies still present one of the fundamental problems in coupling large amounts of horsepower through metallic barriers by use of magnetic (or electric) couplings, namely the generation of power loss and heating due to eddy currents generated by the motion of the magnetic flux through the metallic barrier. Ideally, non-metallic barriers would solve this problem but such materials are not usually acceptable for use in pressure vessel applications due to stringent safety codes. The problem of eddy current generation in metals is well known and, in most applications, has been solved by the use of insulated laminations of magnetically permeable metals as in electric motors and transformers. However, in the past, the use of a laminated barrier in pressure vessels using a magnetic drive has not been accepted due to problems relating to mechanical stability of the laminations in shear and in end thrust.
As an example of a prior art attempt at achieving an acceptable structure see U.S. Pat. No. 1,983,260 (Zorzi, 1934) which illustrates a pressure vessel with an electric motor stator, utilizing the stator as an external support for a laminated cylinder. This arrangement cannot be used for a rotary magnetic coupling using permanent magnets for torque transmission, as such an arrangement requires two concentric rotating members and thus two air gaps, which dictates that the barrier must be self-supporting. In Zorzi the end flanges are retained on the device by a plurality of tie bolts which pass through the stack of laminations. Thus, the pressure rating of the Zorzi vessel would dictate the number and diameter of the tie bolts to achieve sufficient resistance to internal pressure forces; the diameter of the tie bolts would dictate the wall thickness of the laminated stack; and each bolt would have to be insulated to frustrate eddy current effects. In modern magnetic drives for pressure vessels the Zorzi construction would be unacceptable.